1. Field of the Invention
The present invention relates to a heat radiating structure of an electronic device capable of efficiently radiating the heat generated from a heat generating component such as a power source of the electronic device to the exterior of the device and thereby preventing the rise in temperature of the device.
2. Description of the Prior Art
Description is now directed to a conventional heat radiating structure of an electronic device including a heat generating component such as a power source, with reference to FIG. 5 which is a sectional view showing a principal portion of the heat radiating structure. Between an upper metallic shielding case 1 and a lower metallic shielding case 2 is disposed a printed circuit board 3. Electric components such as capacitors or coils are fixed onto the printed circuit board 3 by soldering.
A large number of heat radiating holes 1a are formed in the upper shielding case 1.
A heat sink 7 having a power transistor 5 attached thereto with bolt 6 or the like is fixed onto the printed circuit board 3. A predetermined gap is formed between the upper portion of the heat sink 7 and the upper shielding case 1.
The interior of the electronic device is covered with a shielding case (not shown) disposed around the device.
The interior of the electronic device is partitioned by the printed circuit board 3 into an upper compartment 8 and a lower compartment 9.
According to such a conventional heat radiating structure of the electronic device, when the power transistor 5 attached to the heat sink 7 generates heat while the electronic device is in use, the heat sink 7 absorbs the generated heat and this absorbed heat is radiated to the upper compartment 8 in the electronic device.
When the air present in the upper compartment 8 is heated by the above heat radiation and becomes high in temperature, there occurs a natural convection between this high-temperature air and the outside cold air. As a result of this convection, the high-temperature air present in the interior is discharged to the exterior through the heat radiating holes 1a to prevent an increase in the internal temperature of the electronic device.
In the above conventional heat radiating structure of the electronic device, however, by only such a natural convection as mentioned above, it is difficult for the high-temperature air to be discharged satisfactorily to the exterior through the heat radiating holes 1a, resulting in that the temperature of the air present in the upper compartment 8 becomes high. Consequently, the heat sink 7 also becomes high in temperature to such an extent that it can no longer absorb the heat generated from the power transistor 5, thus giving rise to the problem that the performance of the power transistor is deteriorated.
As the temperature of the upper compartment 8 becomes high, the electric components 4 mounted on the printed circuit board 3 are deteriorated in performance or broken, resulting in deteriorated performance of the entire electronic device.
Moreover, since a large number of heat radiating holes 1a are formed in the upper shielding case 1, the strength of the upper shielding case 1 becomes deteriorated and the gap between the upper shielding case 1 and the power transistor 5 is varied, for example, by vibration of the electronic device, thus giving rise to the problem that it is no longer possible to meet safety standards, etc. In the worst case, the upper shielding case 1 and the heat sink 7 come into contact with each other, leading to generation of noise for example.
There also has been the problem that dust or the like gets into the electronic device through the heat radiation holes 1a formed in the upper shielding case 1.